Control system



Jan. 9, 1934.

F. MOHLER CONTROL SYSTEM Filed Jun 15, 1951 Fig. I.

Inventor.

mg m m M Z m S d m P Patented Jan. 9, 1934 UNITED STATES PATENT OFFICE CONTROL SYSTEM New York Application June 15, 1931. Serial No. 544,521

9 Claims.

My invention relates to control systems, more particularly to control systems for electric motors employed to drive machinery for carrying out predetermined operations upon a material and it has for an object the provision of a simplified, inexpensive and eflicient system of the kind.

More specifically, the invention relates to systems for controlling the operation of motors employed to drive rolling mills and the like in which 10 the finished material emerging from the mill is wound upon a reel, and a particular object of the invention is the provision of a suitable control systcm for maintaining tension in the material between the mill and the take-up reel when the mill is stopped.

In carrying the invention into eifect in one form thereof, the finishing mill motor and the reel motor are supplied from a generator in a Ward- Leonard connection, and means are provided for disconnecting the mill motor from the generator independently of the reel motor upon interruption of the generator field circuit to stop the mill, so that the reel motor remains connected with the generator and sufficiently energized due to the voltage resulting from the residual magnetism thereof to maintain tension in the strip.

More specifically, a control device is provided to weaken and subsequently interrupt the field of the Ward-Leonard generator to stop the mill and means responsive to operation of this control device are provided for disconnecting the mill motor from the generator but leaving the reel motor connected to the generator and energized from the generator voltage due to the residual magnetism thereof, and additional means are provided for connecting a resistance in circuit with the reel motor in response to operation of the control device for limiting the reel motor current to a value which will cause the reel motor to stall although energizing the reel motor to, a sufiicient degree to maint in tension in the strip.

In illustrating the invention in one form thereof, it is shown as embodied in a system for controlling the operation of electric motors employed to drive a mill for rolling cold strip steel and in which the finished strip delivered from the finish-' ing rolls of the mill is wound upon a take-up reel.

For a better and more complete understanding ployed to drive the rolls at the finishing stand and the reel of a cold strip rolling mill.

Referring now to the drawing, a strip 10 of a suitable material such for example as cold steel, is shown as being passed in the direction of the arrow between the rolls 11 of the finishing stand of a cold strip rolling mill. As indicated in the drawing, the thickness or gauge of the strip 10 is reduced by the rolls 11 and the finished strip as it emerges from between the rolls 11 iswound upon a take-up reel 12. The finishing rolls 11 are driven by an electric motor 13 and the reel 12 is driven by a separate electric motor 14.

Although only the finishing stand of the mill and its corresponding driving motor 13 are illustrated in the drawing, it will of course be understood that this invention may be and primarily is intended to be applied to a continuous mill having a plurality of stands, such for example as a tandem mill in which a plurality of separate motors are employed to drive the respective stands of the mill.

The drive motors 13 and 14 are illustrated as being of the direct current shunt wound type; the mill motor 13 being provided with an armature member and with a direct current field winding 15 and the reel motor 14 being similarly provided with an armature and a direct current field winding 16. The field windings 15 and 16 are separately excited from any suitable source of excitation, such for example as that represented in the drawing by the supply line 17 to which the terminals of the field windings 15 and 16 are connected by means of the conductors 18 and 19.

The armatures of the motors l3 and 14 are connected in parallel by means of conductors 20 and 21 respectively to the supply busses 22 which in turn are supplied from a. generator 23 to the armature member of which they are connected by means of conductors 24. The generator 23 is provided with a field winding 25 which is excited from any suitable source of excitation such as that represented by the conductors 17 to which the terminals of the winding 25 are connected by means of the conductors 19, 26, 27 and 28; a suitable variable field weakening resistance shown as comprising the two resistance sections 29 and 30 being included in circuit with the field winding 25.. As thus connected the generator 23 and the motors 13 and 14 constitute a Ward- Leonard control system, i. e., the armatures of the motors l3 and 14 are connected in a closed loop with the armature member of the generator 23 and operate at a speed which is directly proportional to the voltage of the generator as de-' 110 termined by the degree of excitation of its field winding 25.

As is well understood, the generator 23 is driven at a speed, which is preferably substantially constant, by any suitable means such for example as an alternating current synchronous motor (not shown) supplied from any suitable source. Since the drive motor for the generator and the source of supply therefor form no part of the present invention, illustration and further description of these elements is believed to be unnecessary.

An electromagnetic switching device illustrated in the drawing as a contactor 31, under the control of normally closed and normally open contact devices 32 and 33 respectively, serves to establish and interrupt the connections 24 between the armature member of the generator 23 and the supply busses 22. Short circuits about the resistance sections 29 and 30 in the field circuit of the generator 23 are respectively controlled by suitable electromagnetic switching devices such as those represented in the drawing by the contactors 34 and 35 respectively and a similar contactor 36 the lower main contact of which is included in the circuit with the field winding 25 of the generator 23 serves to establish and interrupt the connections between the field winding 25 and the source of excitation 17. A suitable electromagnetic switching device, shown as a contactor 37 serves to establish and interrupt the connection 20 between the arma ture member of the mill motor 13 and the supply busses 22 whilst a similar contactor 38 likewise serves to establish and interrupt the connection 21 between the armature member of the reel motor 14 and supply busses 22. The operation of the accelerating contactors 34, 35, and the disconnect-contactor 36 for the field circuit of the generator, as well as the operation of the mill motor contactor 37, are controlled by a control relay 39 the operation or which in turn is controlled by suitable contact devices, which may be of any suitable type, but which for the purpose of illustration are shown in the drawing as normally closed and normally open switching devices 40 and 41 of the manually operated push button type. The operation or the reel motor contactor 38 is independently controlled by suitable contact devices which likewise may be of any suitable type but which for the purpose of illustration are shown as normally open and normally closed switching devices 42 and 43 respectively of the manually operated push button type.

It will be observed that the contactors 34, 35, 36 and 37 are provided with auxiliary contacts and that interlocking circuits controlled by these auxiliary contacts are provided for controlling the sequence of the opening and closing operations of these contactors. These interlocking circuits are so arranged that the mill motor contactor 3'7 closes before the field circuit contactor 36 and the accelerating contactors 35 and 34 close in the order named after the closing operation of the contactor 36 in response to operation of the start push button 41, whilst these contactors open in the reverse order in response to operation of the stop push button 40. Since the mill motor contactor 3'? is controlled independently of the reel motor contactor 3815? means of the stop and start push button 40 and 41, it will be seen that the mill motor 13 may be disconnected from the generator 23 in response to operation Oi p push button 40 to interrupt the field circuit of the generator while the reel motor 14 remains connected to the generator and sufficiently energized by the voltage of the generator due to the residual magnetism thereof to maintain tension in the strip 10 between the rolls 11 of the finishing stand and the take-up reel 12. It will of course be understood that suitable electroresponsive means, such for example as an undervoltage relay energized by the generator voltage may be employed to disconnect the mill motor from the generator, at a predetermined generator voltage.

A current limiting resistance 44 is included in the connection 21 between the armature member of the reel motor 14 and the supply busses 22 and an electromagnetic switching device shown as a contactor 45 controls a short-circuit about this resistance. It will be observed that the energizing winding of the contactor 45 is interlocked with the mill motor contactor 3'7 and that the contactor 45 is also provided with auxiliary contacts which control interlocking circuits for the contactors 34, 35 and 36; these interlocking circuits being so arranged that the closing of the contactor 45 follows the closing operation of the mill motor contactor 37 and precedes the closing operation of the field circuit contactor 36 whilst in opening the contactor 45 follows the opening operation of the mill motor contactor 37 and is last to open. It will thus be seen that the contactor 45 closes a short circuit about the resistance 44 when the field circuit of the generator 23 is completed and that this contactor 45 opens the short circuit about the resistance 44 and thereby reinserts this resistance in circuit with the arma-. ture of the reel motor 14 when the field circuit or the generator 23is interrupted. The ohmic value of the resistance 44 is so chosen that it limits the current supplied to the reel motor 14 to a safe value but which nevertheless, sufliciently energizes the reel motor 14 to cause it to maintain the desired amount of tension in the strip 10.

Suitable field weakening resistances 46 and 4'7 are respectively connected in circuit with the field windings 15 and 16 of the mill motor 13 and reel motor 14 and these resistances may be varied by means of respectively cooperating movable contact members 48 and 49 which as shown are mechanically connected with each other to provide for simultaneous movement of members 48 and 49 when either one is moved.

'During the acceleration, deceleration and full speed rolling operation of the mill, the tension in the strip 10 between the rolls 11 of the finishing stand and the reel 12 is controlled by means of a suitable tension regulating device 50 which is in reality a constant load orconstant current regulator and which functions in a well understood manner to maintain the load on the reel motor 14, and consequently the tension in the strip 10, substantially constant at a value which may be adjusted as desired by means of a variable resistance 51 included in the energizing circuit of the regulating device 50.

With the above understanding of the elements, apparatus and connections and their organization in the system, the operation of the system itself will readily be understood from the detailed description which follows: To start the nilll, the start button 33 is momentarily depressed to complete an energizing circuit for the generator contactor 31; this energizing circuit being traced from the lower supply line 1'7 through the operating winding of the contactor 31, start button 33 in its closed position to the upper supply line 17. Contactor 31 closes in response to the energization of its operating coil and completes the connection 24 between the armature member of the generator 23 and the supply busses 22. The lower auxiliary contacts of contactor 31 complete a holding circuit for the operating coil of the contactor through the normally closed contacts of the stop button 32 independently of the start button 33 which may now be released.

After the generator 23 has been connected to the supply busses 22, the start button 41 is depressed to complete an energizing circuit for the control relay 39 which circuit may be traced from one side of the supply lines 19 (which are connected to the supply source 17) through the contacts of the start button in its closed position, the operating winding of the relay 39, and thence to the opposite side of the supply lines 19. Control relay 39 in responding to the energization of its operating winding moves to the upper or closed position in which its upper auxiliary contact establishes a holding circuit for the operating coil through the normally closed contacts of the stop button 40 independently of the start button 41 which may now be released. Relay 39 in its closed position completes an energizing circuit for the operating coil of the mill motor contactor 37; this circuit being traced from the lower supply line. 17 through the operating coil of the contactor 37, conductor 52, contact 39a of relay 39 (in its closed position) and thence by conductors 53 and 19 to the upper supply line 17. Mill motor contactor 37 in responding to the energization of its operating coil moves to its upper or closed position in which it connects the armature member of the mill motor 13 with the supply busses 22 and its upper auxiliary contact in the closed position completes an energizing circuit for. the stalling resistance contactor 45 which extends from the lower side of the supply line 17 through the upper auxiliary contacts 01' contactor 37, operating coil of contactor 45 to the upper side o1 supply line 17.

In response to the energization of its operating winding, contactor 45 moves to its upper position in which its lower contacts complete a short circuit about the stalling resistance 44 and its upper auxiliary contact completes an energizing circuit for the field contactor 36 of the generator; this energizing circuit being traced from the lower side of the supply source 17 through upper auxiliary contacts of the contactor 45, conductor 54, operating coil of contactor 36. intermediate contact 39b of relay 39 (in the closed position) and thence by conductors 53 and 19 to the upper side of the supplyisource 17. Field contactor 36 thereupon closes its lower main contact to completea circuit for the field winding 25 of the generator 23 with the field weakening resistances 29 and 30 in circuit therewith. In its closed position a lower auxiliary contact of contactor 36- establishes an energizing circuit for the accelerating contactor 35; this circuit being traced from one side of the line 19 through the lower auxiliary contact 36 in its closed position, operating winding of contactor 35, intermediate contact 390 of relay 39 (in its closed position) to the opposite side of the line 19. In its closed position the contactor 35 short circuits the resistance section 3t) thereby increasing the excitation of the field winding 25 of the generator andlikewise increasing the generator voltage. The lower auxiliary contact of accelerating contactor 35 in its closed position also completes an energizing circuit for the contactor 34, this circuit being traced from circuits the final section 29 of the field weakening resistance thereby further increasing the excitation of the field winding 25 of the generator and likewise increasing the generator voltage to its full value. Although only two contactors 34 and 35 are shown for short circuiting the field weakening resistances 29 and 30, it will be understood that the field weakening resistance may be divided into as many sections as desired and that a corresponding number of contactors may be employed successively to short circuit the resistance sections. It will be observed that the final accelerating contactor 34 is provided with an upper auxiliary contact which completes a holding circuit for the energizing winding of the contactor 35 independently of the contact 390 of relay 39,- and that contactors 35 and 36 are likewise provided with a number of auxiliary contacts which respectively complete holding circuits for the operating winding of contactors 36 and 37 independently of contacts 39b and 393. respectively of the relay 39.

At this point in the operation the generator will be developing full voltage and the mill motor 13 will consequently be operating at full speed. In the case of a tandem mill in which a plurality of mill motors similar to the mill motor 13 are employed to drive the various stands of the mill, it will be understood that a separate contactor similar to the mill motor contactor 37 will be provided for each of the remaining mill motors and that these remaining contactors will be con.- nected in parallel with the contactor 37 so that all will be simultaneously operated to the closed position to connect all the mill motors to the supply line 22.

The operator now threads the strip 10 through the reducing rolls at the various stands of the mill and finally through the reducing rolls 11 at the finishing stand, after which the strip 10 is carried along and the end is inserted in the jaws of the reel 12 after which the reel motor 14 is started by momentarily depressing the start button 42 to complete an energizing circuit for the operating coil of the reel motor contactor 38; this circuit being readily traced from the upper side of the supply source 17 through the contacts of the start button 42 in its closed position, operating coil of contactor 38 and thence to lower side of the supply source 17. The contactor 38 in responding to the energization of its operating coil closes its main contact to connect the armature member of the reel motor 14 to the supply busses 22 and the reel motor 14 thereupon accelerates quickly to take up the slack in the strip 10 between the rolls 11 at the finishing stand and the reel 12 and thereafter the tension regulating device 50 maintains the desired value of tension in the strip. Contactor 38 in closing completes a holding circuit for its operating coil which may be traced from the upper side of the supply source 17 through the normally closed contacts of the stop button 43, auxiliary contacts of contactor 38,

operating coil of the contactor and thence to the If it should be desired to stop the mill at any point in the rolling operation without losing the tension in the strip 10 it is only necessary to depress the stop button 40 to interrupt the energizing circuit of the control'relay 39 which falls under the attraction of gravity to its lower position in response to the deenergization of its operating coil. Contactors 35, 36, and 37 are not opened immediately since, as previously pointed out, holding circuits have been established for the operating coils of these contactors independently of the contacts of the relay 39. However, lowermost contact 39a of relay 39 interrupts the energizing circuit of accelerating contactor 34 which thereuponppens and removes the short circuit from about the resistance section 29 thereby decreasing the excitation of the field winding 25 of the generator and likewise decreasing the generator voltage in proportional amount. The mill motor 13 and the reel motor 14 are decelerated in response to the decreased generator voltage and the tension in the strip 10 is maintained constant at the predetermined desired value by means of the tension regulator 50.

In its open position, the auxiliary contact of accelerating contactor 34 interrupts the holding circuit for the contactor 35 which thereupon opens and removes the short circuit from about the resistance section 30 thereby further decreasing the excitation of the field winding 25 and likewise further decreasing the generator voltage as a result of which the speed of the mill motor 13 and reel motor 14 is further decelerated to a very low value; tension in the strip 10 being still maintained constant by the tension regulator 50. In its open position, the upper auxiliary contact of contactor 35 interrupts the holding circuit for the field contactor 36 which thereupon drops to its open position in which it interrupts the circuit for the field winding 25 of generator 23, as a result of which the generatorvoltage is decreased to a value that is determined solely by the residual magnetism of the pole pieces of the generator.

When the field contactor 36 drops to its open position its upper auxiliary contact interrupts the holding circuit for the mill motor contactor 37 which thereupon falls to its lower or open posi tion in which it disconnects the mill motor 13 from the supply busses 22 and consequently from the generator 23, It will be observed, however, that the armature member of the reel motor 14 remains connected to the supply busses 22 since the connections between this motor are not disturbed by the operation of the stop button 40 to disconnect the mill motor 13 from the generator 23 and to interrupt the field circuit of the latter. Consequently, the reel motor 14 remains connected to the generator 23 and is sufliciently energized by the current generated due to the residual magnetism of the generator to maintain tension in the strip 10 while the mill is stopped. When the mill motor contactor 3'7 opens,its upper auxiliary contact interrupts the energizing circuit of the stalling resistance contactor 45 which thereupon descends to its open position to remove the short circuit from about the stalling resistance 44. If no additional resistance were included in the armature circuit of the reel motor 14 when the mill motor is stopped, the voltage generated by the generator 23 due to its residual magnetismmight be sufflcient to cause the reel motor 14 to rotate and rupture the strip 10 between the rolls 11 of the finishing stand and the reel 12. As previously pointed out, however, the stalling resistance 44 is designed to limit the current supplied to the motor 14 when the mill motor is stopped, to a value which causes the reel motor 14to stall but which nevertheless provides sutficient energization for the motor 14 to cause it to maintain the desired value of tension in the strip.

To resume the rolling operation it is only necessary to depress the start button 41 whereupon the sequence of operation previously described in response to the operation of this button will follow and the rolling operation will proceed.

It will thus be seen that when the mill is stopped, the reel motor 14 is maintained energized by the voltage generated by the generator due to the residual magnetism thereof and that tension is consequently maintained in the strip when the mill is stopped.

Although .in accordance with the provisions of the patent statutes, I have described this invention as embodied in specific apparatus and connections, I would have it understood that the specific apparatus and connections shown in the drawing and described in the specification are merely illustrative and that the invention is by no means limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of the invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination with a strip of material, a mill motor for operating upon the material, a reel motor for winding the finished strip, a variable voltage generator for supplying said motors, means for decreasing the voltage of said generator to stop said motors, and means responsive to an operation of said voltage decreasing means for disconnecting said mill motor from said generator independently of said reel motor so that said reel motor remains connected to said generator and is thereby energized to maintain tension in the strip.

2. In combination with a strip of material, a mill motor for operating upon said strip, a reel motor for winding finished strip, a generator having its armature connected in a closed loop with said motors, means for reducing the excitation of said generator to decelerate said motors, and means responsive to said excitation reducing operation for disconnecting said mill motor from said generator independently of said reel motor sothat the latter remains connected to said generator andis thereby energized by the reduced excitation thereof to maintain tension in said strip after the mill motor has stopped.

3. In a motor control system for a strip rolling mill and the like comprising in combination, a mill motor for operating upon a strip of material, a reel motor for winding finished strip, a supply generator provided with a fleld circuit for supplying said motors, load responsive control means for said reel motor for maintaining constant tension in said strip during operation of said mill, means for interrupting said field circuit to decelerate said motors, and means responsive to interruption of said field circuit for disconnecting said mill motor from said generator independently or said reel motor so that the latter remains connected to said generator and is thereby energized due to the residual magnetism thereof to maintain tension in said strip.

4. A motor control system for a cold strip rolling mill and the like comprising in combination, a mill motor for operating upon a strip 0! material, a reel motor for winding finished strip, a supply generator provided with a field circuit and a variable resistance included therein, connections between said generator and said motors, means for increasing said resistance to decrease the voltage of said generator and the speed or said motors, means responsive to operation of said resistance increasing means for interrupting said field circuit to stop said mill motor, means responsive to interruption of said field circuit for disconnecting said mill motor from said generator independently of said reel motor so that the latter remains connected to said generator and energized due to the residual magnetism thereof, and means for limiting the current supplied to said reel motor after interruption of said field circuit so that said reel motor is caused to stall but is sufficiently energized to maintain tension in the strip.

5. A motor control system for a strip rolling mill and the like comprising in combination a mill motor for operating upon the strip, a reel motor for winding finished strip, a supply generator provided with a field circuit and having its armature connected in a closed loop with said motors, a resistance included in said field circuit, a switch for controlling the stopping of said motors, a contactor responsive to operation of said stopping switch to include saidresistance in said field circuit to decelerate said motors, a contactor responsive to operation of said stopping switch to interrupt said field circuit, a second contactor responsive to interruption of said field circuit for disconnecting said mill motor from said generator independently of said reel motor so that the latter remains connected to said generator and sufiiciently energized due to the residual magnetism thereof to maintain tension in the strip, and means responsive to operation of saidstopping switch to limit the current vice, and electromagnetic switching mechanism controlled thereby for interrupting said field circuit to decelerate said motors and for subsequently disconnecting said mill motor from said generator while maintaining said reel motor connected to said generator and sufficiently energized due to the residual magnetism thereof to maintain tension in the strip.

7. In a motor control system for strip rolling mills and the like, a mill motor for operating upon a strip of material, a reel motor for winding finished strip, a supply generator provided with a field circuit, connections between said reel motor and said generator, an electromagnetic switching device for connecting and disconnecting said mill motor and said generator, a second electromagnetic switching device for establishing and interrupting said field circuit, control devices for said switching devices and electrical connections controlled by said control devices for causing said first mentioned switching device to connect said mill motor and said generator prior to operation of said second device to establish said field circuit and for causing said second switching device to interrupt said field circuit and said first switching device to subsequently disconnect said mill motor and generator without interrupting said reel motor connections so that said reel motor is maintained subsequently energized by the residual magnetism of said generator to maintain tension in said strip.

8. In a motor control system, a first motor for operating upon a length of material, a reel motor for winding finished material, a supply generator provided with a field circuit, a current limiting resistance connected with said reel motor, connections between said reel motor and said generator, a contactor for controlling said resistance, a second contactor for connecting and disconnecting said first motor and said generator, a third contactor for establishing and interrupting said field circuit, control devices for said contactors, and electrical interlocking connections controlled thereby for causing said contactors to render said resistance ineffective, connect said first motor to said generator and establish said field circuit, and to perform the reverse operations in the reverse order without interrupting 9. In a motor control system, the combination with a first motor for operating upon a length of material, a reel motor for winding finished material, a supply generator provided with a field circuit,a field weakening resistance included in said circuit, electrical connections between said reel motor and said generator and a current limiting resistance included in said connections, a first contactor for connecting said first motor to said generator, a second contactor for short circuiting said current limiting resistance, electromagnetic switching mechanism for establishing and interrupting said field circuit and short circuiting said field weakening resistance, start and stop control devices for said contactors and switching mechanism, and electrical circuits controlled by said control devices and interlocking circuits for causing said contactors to connect said mill motor to said generator and short circuit said current limiting resistance, said switching mechanism to establish said field circuit and short circuit said field resistance and to. cause said contactors and switching mechanism to perform the reverse operations in the reverse order without interrupting said reel motor connections so that the latter remains connected to said generator with said current limiting resistance in circuit and sufiiciently energized due to the residual magnetism of said generator to maintain tension in said length of material. FRANCIS MOHLER. 

